By activating the Settings control, which is on the very same page as your inbox. Then, once that control is activated, the See all settings button.  Once you are in settings, going to the Forwarding and POP/IMAP tab, then activating the Disable forwarding radio button, then activating the Save Changes button.

The default landing page when you open Gmail is the inbox page.
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Brian - Windows 10 Pro, 64-Bit, Version 20H2, Build 19042  

One does not discover new lands without consenting to lose sight of the shore for a very long time.

           ~ André Gide